Recently, data is converted into numerical values, processed by computers, and displayed on display units or printed as images by printers in a variety of fields. Therefore, to allow a display unit or printer as an output apparatus to correctly detect transmitted data, a communication scheme (protocol) or format must be set.
This will be described below by taking an output system using DICOM (Digital Imaging and Communications in Medicine) which is a medical image communication protocol as an example.
<System Configuration>
FIG. 5 shows an example of the configuration of an output system using DICOM as a communication protocol.
A host computer 401 and an output apparatus 402 are connected by a communicating means 403. Output parameters and output data are transferred from the host 401 to the output apparatus 402.
As the communicating means 403, a computer network such as Ethernet, serial communication such as RS-232 or USB, or parallel communication such as SCSI or GPIB is used.
The arrangement of the host 401 will be described first.
A CPU 411 performs various internal processes of the host 401 and thereby controls the entire host.
A storage unit 412 stores data to be output. As this storage unit 412, a memory such as an SRAM or DRAM, a fixed storage such as a hard disk, or a removable storage such as a floppy disk or MO is used.
An output parameter lookup table 413 stores output parameters used when the output apparatus 402 outputs data. As this output parameter lookup table 413, a memory such as a ROM or RAM, a fixed storage such as a hard disk, or a removable storage such as a floppy disk or MO is used.
A data processor 414 converts and processes data, stored in the storage unit 402, in accordance with the output parameters. This data processor 414 may be implemented by hardware such as an ASIC. Alternatively, the data processor 414 may be implemented by software, and the CPU performs actual processing.
An I/F unit 415 connects the host 401 and the communicating means 403. This I/F unit 415 can be implemented by either hardware or software in accordance with the type of the communicating means 403.
The arrangement of the output apparatus 402 will be described next.
This output apparatus 402 actually displays or prints out data in accordance with the output parameters transferred from the host 401.
An I/F unit 421 connects the output apparatus 402 and the communicating means 403. Like the I/F unit 415, this I/F unit 421 may be implemented by either hardware or software.
An output parameter storage 422 stores the output parameters defined and transferred by the host 401 and is looked up when an output unit 425 outputs data. As this output parameter storage 422, a memory such as an SRAM or DRAM or a fixed storage such as a hard disk is used.
A buffer storage 423 buffers data processed and transferred by the host 401, before the output unit 425 outputs data. As this buffer storage 423, a memory such as an SRAM or DRAM or a fixed storage such as a hard disk is used.
The output unit 425 actually outputs data transferred from the host 401. Examples of this output unit 425 are a monitor display and a printer.
<Data>
Data processed by the above system contains actual information and attached information.
In the DICOM format, the actual information is image data. Images photographed by, e.g., X-rays, CT, and MR are stored in various formats. Each image data is represented by monochrome data of 8 bits (or less), monochrome data of 16 bits (or less), or color data of 8 bits (or less) for each color, in accordance with a format designated in the attached information.
The attached information relates to the image format of the actual information, conditions (input conditions) when the actual information is formed, and conditions (output conditions) when the actual information is output. The information concerning the image format includes, e.g., the image size, the number of gray levels per pixel, the image mode indicating whether the image is monochrome or color, the maximum density, the pixel construction method (data storage method) when one pixel is constructed by a plurality of data, and the dynamic range of density.
Examples of the input conditions are the input date/time, the manufacturer, type, and serial number of the input modality (apparatus), the input person, the input environment (e.g., temperature and humidity), the input location, the information (e.g., the name, date of birth, and object ID) pertaining to the photographed person, and the photographed portion.
Examples of the output conditions are the output medium, the image processing method (e.g., the extrapolation method and the tone correction method), the output method (the algorithm and superposition of outputs when data is actually output), the output mode (e.g., a high-speed mode or high-resolution mode), the manufacturer, type, and serial number of the output apparatus, the output person, the output location, and the output date/time.
<Parameters>
In the above system, output parameters are output conditions set when the output apparatus 402 outputs data.
Diverse output parameters are used in accordance with the type of output apparatus. For example, when the output apparatus 402 is an inkjet printer, output parameters are the type of ink, the density of ink, the method of combining inks, the ink residual amount/full tank detecting mechanism, the recovery sequence, the image processing algorithm (e.g., the extrapolation method and the tone correction method), the number of times of overlay printing (the number of passes) before output completion, and the type and size of output medium (e.g., paper or film).
<Flow Chart>
Processing until data is output in the conventional output system with the above configuration will be described below with reference to a flow chart in FIG. 7 which shows the processing steps of the output apparatus. This data output is performed by two stages: parameter setting operation and data output operation.
In the parameter setting operation, the host 401 extracts desired parameters from the output parameter lookup table 413. To transfer the extracted parameters to the output apparatus 402 via the communicating means 403, the host 401 transfers the parameters to the I/F unit 415.
These parameters transferred to the output apparatus 402 are input via the I/F unit 421 (step S71) and stored in the output parameter storage 422 (step S72). In this way, the parameter setting operation is completed (step S73).
The data output operation is then executed. In the host 401, data stored in the storage unit 412 is read out, and the readout data is converted and processed in accordance with the previously selected output parameters. The converted and processed data is transferred to the communicating means 403 via the I/F unit 415.
The output apparatus 402 receives the data from the communicating means 403 via the I/F unit 421 (step S74). The received data is converted into a form which can be output by the output unit 425, by referring to the output parameters stored in the output parameter storage 422 (step S75). The data thus converted into the format that can be output is sent to the buffer storage 423 and temporarily stored in it (step S76). If the output unit 425 is capable of output, the output unit 425 extracts the data from the buffer storage 423 and actually outputs the data (step S77).
FIG. 6 shows another arrangement of the output apparatus in the conventional output system. This output apparatus 501 has a parameter lookup table 522 and image processor 514, in addition to the arrangement of the output apparatus 402 shown in FIG. 5.
When this output apparatus 501 is to output data, output parameters are first set. That is, a host computer or the like designates output parameters in the parameter lookup table 522 via a communicating means 502. The designated output parameters are stored in a parameter storage 512. In this manner, the setting process of this output apparatus 501 is completed.
When the setting is completed, output data to be actually output is transferred from the communicating means 502 via an I/F unit 511. The transferred output data is temporarily stored in a storage unit 513. An image processor 514 sequentially reads out the data stored in the storage unit 513, and processes the readout data into a desired data format in accordance with the output parameters stored in the parameter storage 512. An output unit 515 outputs the data processed into the desired format, and the output operation is completed.
If the output unit 515 is incapable of output, the storage unit 513, for example, buffers the data.
The medical output system as described above often uses a printing apparatus (printer) as the output apparatus. Although various types of apparatuses are known as printers, an inkjet printer which prints data by discharging a printing agent onto a printing medium is recently extensively used. This is so because the structure is suited to cost reduction and improvements of the performance are remarkable.
To increase the printing speed or the like of an inkjet printer, a nozzle row in which a plurality of ink discharge orifices (nozzles) for discharging ink of the same type are arrayed is formed for each ink of the same color but different in density, or for each of different colors. Also, a tone can be expressed by changing the discharge amount of ink of the same type by a plurality of stages.
An inkjet printer prints data by moving a printhead having these nozzle rows relative to a printing medium and at the same time discharging ink from the nozzles. As printing methods of an inkjet printer, a so-called serial printing method and a so-called full-line printing method are put to practical use. In the former method, nozzle rows are arranged substantially parallel to the convey direction of a printing medium. A printing medium is intermittently conveyed, and, while this printing medium is stopped, data is printed by driving the nozzles and at the same time moving the printhead in a direction substantially perpendicular to the array direction of the nozzle rows. In the latter method, nozzle rows are so fixed as to cover the printing width of a printing medium. Data is printed by driving the nozzles while a printing medium is moved at a constant velocity in a direction perpendicular to the nozzle rows.
When images are printed by these methods, a pixel is defined as a unit for forming an image. This pixel need not be made up of one dot formed on a medium by one-time ink discharge from one nozzle; a pixel may also be made up of a plurality of dots. When a pixel is made up of a plurality of dots, these dots may be printed as they overlay in substantially the same point, or may be printed in adjacent points. In either case, dot positions are determined in accordance with predetermined rules.
An image processing means performs processing such as enlarging interpolation or reduction for image data to be printed, such that the data has an image size suited to a printing apparatus. Subsequently, the color and density to be printed are determined for each pixel in accordance with predetermined rules. The data is printed on the basis of this determination.
In this data printing, one pixel may be made up of a plurality of dots as described above. Hence, a plurality of types of inks differing in density can be chosen as inks used to print each pixel. When a variable-discharge-amount head is used, the discharge amount, i.e., the ink amount used to print a dot can be changed. These two methods may also be combined.
Furthermore, as a method of faithfully reproducing the tone of an image when the image is printed, a halftone processing method such as a dither method or an error diffusion method is used. In this dither method or error diffusion method, the number of gray levels to be expressed can be increased by increasing the number of gray levels of one pixel. A practical example of this printing method is described in, e.g., Japanese Patent Laid-Open No. 10-324002 (U.S. Pat. No. 6,164,747).
In this method, a plurality of types of inks can be discharged for one color, and each pixel is expressed by selectively discharging (overlaying) ink droplets a plurality of times within a predetermined limit. For example, the number of gray levels of the printing density of, e.g., an OD value (transmission density) can be increased. More specifically, when a printhead capable of discharging inks of six different densities is used to overlay dots four times or less for each pixel at 600 dpi, 50 or more gray levels can be expressed under the restriction that no ink dots of the same density are overlaid. Also, 200 or more gray levels can be expressed when each pixel is made up of 2×2 adjacent points and ink dots are overlaid 16 times or less. In either case, the number of gray levels that can be expressed can be increased by overlaying ink dots of the same density.
It may of course also be possible to express a tone by varying the ink amount of dot by varying the amount of ink discharged from a nozzle, instead of discharging inks of different densities as described above. A tone may also be expressed by combining these methods.
In these methods, a rule indicating the correspondence between the density (desired OD value) of a pixel to be expressed and the ink overlaying method is predetermined. In accordance with this rule, actual printing, i.e., the nozzle and the timing of ink discharge are determined. A printing control means performs actual printing in accordance with the determination.
As an example, printing OD values as pixel densities when printing is actually performed by different inks are measured, and a printing OD value when overlay printing is performed is calculated from the measurement values. A table describing the printing OD values of pixels in one-to-one correspondence with the overlay printing combination is prepared. An overlay printing combination by which a printing OD value close to the desired OD value of a pixel to be printed is obtained is chosen. In the error diffusion process, a difference between the desired OD value of a pixel to be printed and the printing OD value in the table is calculated, and this difference is distributed as an error to adjacent pixels.
The conventional output system is constructed as above. When the output apparatus is to output data, therefore, the host first transmits data concerning parameters for setting the output apparatus and then actually transmits output data. Hence, data transfer is performed a plurality of times, and this requires user's labor and a long time before data is actually output.
Also, since the setting of the output apparatus and the transfer of output data are separately performed, the two processes cannot be matched in some cases. For example, parameters not matching the characteristics of output data may be transmitted to the output apparatus, or output data alone may be transmitted without setting parameters. As a consequence, the output data is output under output conditions which are not optimum
Furthermore, when high-quality output is required, a large number of various parameters must be set. Since this complicates the setting of the output apparatus, expert knowledge is necessary.
This situation will be considered by taking a case in which a printing apparatus is used as an output apparatus in a medical output system as an example. Many types of modalities such as DR (an X-ray photographing apparatus), CT, MR, and US are used to generate medical images.
DR acquires digital image data in conventionally performed X-ray photographing and has various types. Examples are a modality by which an output image from I.I. (Imaging Intensifier) is converted into a digital signal, a modality by which an imaging plate on which a latent image is formed by X-ray photographing is scanned with a laser beam and converted into a digital signal, and a modality by which an image obtained by X-ray photographing is converted into a digital signal by a sensor. CT and MR obtain digital data of a tomographic image of a human body by using X-rays and magnetism, respectively. US obtains a signal of a tomographic image of a human body by using ultrasonic waves.
When hard copies are to be obtained from image data generated by these modalities by using a printer as the output apparatus, the necessary specifications largely change from one modality to another. Many images generated by DR have relatively gradually changing tones. Also, since objects to be diagnosed by DR are light shades, the acquired image data often has 1,000 or more gray levels, so the number of gray levels of hard copies must also be 1,000 or more. On the other hand, the number of gray levels obtained by CT, MR, and US is about 256 to 512, and many images obtained by these modalities have relatively abruptly changing tones. Accordingly, the number of gray levels of hard copies need only be about 256 to 512.
A printer which forms hard copies from these image data generally takes a long processing time if the number of gray levels to be expressed is large, regardless of the printing method.
In the conventional medical output system, a dedicated printer is connected to each of such modalities. Therefore, an optimum printer is selected and connected to each modality, or printing parameters of a printer are set in advance so as to be optimum for a connected modality.
With the recent advance of networks, however, a plurality of modalities are often connected to the same network to share a single printer connected to that network. Even in a case like this, it is desirable to print data by setting optimum parameters for each modality.
For example, to print a DR image requiring a large number of gray levels, the number of gray levels of a hard copy must be increased; to print a CT, MR, or US image requiring a relatively small number of gray levels, decreasing the number of gray levels is effective to shorten the overall processing time.
To meet this demand, it is possible to prepare a plurality of tone processing methods and form a hard copy by using an optimum tone processing method in accordance with the modality used. It is also favorable to be able to form a hard copy by necessary and sufficient tone processing in accordance with the department which has requested examination, the purpose of examination, and the purpose of use of a hard copy. Furthermore, it is favorable to be able to select a necessary and sufficient one of not only tone processing methods but also types of printing media to be used.
Unfortunately, if tone processing and a printing medium can be changed in accordance with the type of modality or the purpose of use as described above, a user must perform various settings of a printing apparatus by using a keyboard or the like before the printing apparatus can output data. After these settings, the user instructs the printing apparatus to actually print the data.
In this case, therefore, a number of diverse settings must be performed. Since this complicates the settings of the printing apparatus, expert knowledge is required.